Arterial diseases and injuries are common and have severe consequences including amputation or death. Atherosclerosis, in fact, is a major problem in the aged population, particularly in the developed countries.
Atherosclerosis of the lower extremities (often, otherwise, referred to as peripheral vascular disease) is a common disorder that increases with age, ultimately affecting more than 20% of those people over the age of 75. Lesions resulting from atherosclerosis are often characterized by diffuse and multi focal arterial stenosis and occlusion.
Peripheral vascular disease often manifests itself as an intermittent insufficiency or claudication of blood flow in calf, thigh or buttocks. The symptoms of claudication often result from an inability of the body to increase blood flow during exercise.
In more extreme cases of peripheral vascular disease, blood flow of even a resting patient may be insufficient to meet basal metabolic needs of the extremities. Symptoms of blood flow insufficiency in these areas may include pain in the forefoot or toes or, in extreme cases, non-healing ulcers or gangrene in the affected limb.
One of the most effective means of diagnosing and treating atherosclerosis is based upon the use of magnetic resonance angiography (MRA) to create images of portions of the vascular system. As is well known, MRA is a form of magnetic resonance imaging (MRI) which is especially sensitive to the velocity of moving blood. More specifically, MRA generates images by relying upon an enhanced sensitivity to a magnitude and phase of a signal generated by moving spins present within flowing blood.
MRA, in turn, can be divided into three types of categories: 1) time of flight (TOF) or inflow angiography; 2) phase contrast (PC) angiography (related to the phase shift of the flowing proton spins) and 3) dynamic gadolinium enhanced (DGE) MRA. While the three types of MRA are effective, they all suffer from a number of deficiencies.
The predominant deficiency of all three types of existing MRA techniques relates to speed of data collection. For example, patient motion is known to significantly degrade image quality of TOF MRA. To avoid image degradation, a patient undergoing DGE MRA is typically required to hold his breath during data collection. PC MRA relies upon the use of long time-to-echo (TE) intervals for signal sampling that result in other T2 effects that tend to degrade image quality. Because of the importance of MRA, a need exists for MRA methods that are less reliant upon time or upon movement of the patient.